From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 950A1FDEE27 for ; Thu, 23 Apr 2026 16:43:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0A5666B008C; Thu, 23 Apr 2026 12:43:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0560B6B0092; Thu, 23 Apr 2026 12:43:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ED5A56B0093; Thu, 23 Apr 2026 12:43:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id DDDB46B008C for ; Thu, 23 Apr 2026 12:43:30 -0400 (EDT) Received: from smtpin10.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay03.hostedemail.com (Postfix) with ESMTP id A9C8BA033F for ; Thu, 23 Apr 2026 16:43:30 +0000 (UTC) X-FDA: 84690391380.10.7194419 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) by imf05.hostedemail.com (Postfix) with ESMTP id C40B6100006 for ; Thu, 23 Apr 2026 16:43:28 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=uiOc+nuX; spf=pass (imf05.hostedemail.com: domain of jp.kobryn@linux.dev designates 95.215.58.181 as permitted sender) smtp.mailfrom=jp.kobryn@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776962609; a=rsa-sha256; cv=none; b=VEuFyfW76LdemzV4SzZuMVSso7G3WpTKK4gnyW5eF474xqNdjUz0t5I5fdRML8MbN8TQ6U U0WxnZLMbOh2kbI8eAAbts3FDR/BSlIon1BdjfXhsxRNzUiAyfsbQDoVDlf/c+jiKGfzwF I0TlWxFf4nAMJxNOJ4yHSHPFqDfLH6w= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=uiOc+nuX; spf=pass (imf05.hostedemail.com: domain of jp.kobryn@linux.dev designates 95.215.58.181 as permitted sender) smtp.mailfrom=jp.kobryn@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1776962609; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=YIEKJZNSJ9OeiPhU0FRTZ02fkQczRvgGzar+b8miLXs=; b=4D5WHqkLlfbZyOl0wGXtmy+S/bUAYjSAoYufULYqoPgIgMBDcCq1FZpyYdZutf6a4BHsck NFf6KK/Duo1xSIYo8wWsVhtTg4Ch5cgOHjhlNUg3F1wFJMaWRGnlhFxAnyPNtiLdNuIJPJ MBsHi95uA7FGqA4lA2fqKbrBUFfiB9M= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776962606; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=YIEKJZNSJ9OeiPhU0FRTZ02fkQczRvgGzar+b8miLXs=; b=uiOc+nuXzSkMncpve1zOJ6r496DTBRy1/LeDDBTNkjhQpJo2WLQS+blMYN8XGaT3LahYpP hWqco+oyHmjT0KloyqDD2j/TW7JejM/aS+RULQ+E1dvoy822/ISmZPAg6AtWQBSsHYD7QI nssqrwS/t1gyYa2StGfPWMMWSBvuKWg= From: "JP Kobryn (Meta)" To: linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@kernel.org, mhocko@suse.com, willy@infradead.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, riel@surriel.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, youngjun.park@lge.com, qi.zheng@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH] mm/lruvec: preemptively free dead folios during lru_add drain Date: Thu, 23 Apr 2026 09:43:07 -0700 Message-ID: <20260423164307.29805-1-jp.kobryn@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: C40B6100006 X-Stat-Signature: x3bpah14xs8xcnmbd8wg67ofqhmmzbtq X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1776962608-229857 X-HE-Meta: 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 mcSz8IPa ty4sd0WRzd+xNQHF6/0i14BhvXMGxJDKjVPvnlEFuKgV7WH2AXjsF9EngbRmK/doEnrbip/wholFzfeKQUw+9bKrGlV+tM72uHiKDLNMesuRGe9m1wFE8EYOAeOkQT53XywmAV1kdkSnIx74c4k1gvmOBSJo/r4MaJhpRtNQsPolpyj4UPgLAYo34OICVuqNkdjTIqcU4g6U8Mrd9lC1L6JFx0nu+O2Za9+28I/JGmpyN+cWpnY3IHs+63g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Of all observable lruvec lock contention in our fleet, we find that ~24% occurs when dead folios are present in lru_add batches at drain time. This is wasteful in the sense that the folio is added to the LRU just to be immediately removed via folios_put_refs(), incurring two unnecessary lock acquisitions. Eliminate this overhead by preemptively cleaning up dead folios before they make it into the LRU. Use folio_ref_freeze() to filter folios whose only remaining refcount is the batch ref. When dead folios are found, move them off the add batch and onto a temporary batch to be freed. During A/B testing on one of our prod instagram workloads (high-frequency short-lived requests), the patch intercepted almost all dead folios before they entered the LRU. Data collected using the mm_lru_insertion tracepoint shows the effectiveness of the patch: Per-host LRU add averages at 95% CPU load (60 hosts each side, 3 x 60s intervals) dead folios/min total folios/min dead % unpatched: 1,297,785 19,341,986 6.7097% patched: 14 19,039,996 0.0001% Within this workload, we save ~2.6M lock acquisitions per minute per host as a result. System-wide memory stats improved on the patched side also at 95% CPU load: - direct reclaim scanning reduced 7% - allocation stalls reduced 5.2% - compaction stalls reduced 12.3% - page frees reduced 4.9% No regressions were observed in requests served per second or request tail latency (p99). Both metrics showed directional improvement at higher CPU utilization (comparing 85% to 95%). Signed-off-by: JP Kobryn (Meta) --- mm/swap.c | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) diff --git a/mm/swap.c b/mm/swap.c index 5cc44f0de9877..71607b0ce3d18 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -160,13 +160,36 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) int i; struct lruvec *lruvec = NULL; unsigned long flags = 0; + struct folio_batch free_fbatch; + bool is_lru_add = (move_fn == lru_add); + + /* + * If we're adding to the LRU, preemptively filter dead folios. Use + * this dedicated folio batch for temp storage and deferred cleanup. + */ + if (is_lru_add) + folio_batch_init(&free_fbatch); for (i = 0; i < folio_batch_count(fbatch); i++) { struct folio *folio = fbatch->folios[i]; /* block memcg migration while the folio moves between lru */ - if (move_fn != lru_add && !folio_test_clear_lru(folio)) + if (!is_lru_add && !folio_test_clear_lru(folio)) + continue; + + /* + * Filter dead folios by moving them from the add batch to the temp + * batch for freeing after this loop. + * + * Since the folio may be part of a huge page, unqueue from + * deferred split list to avoid a dangling list entry. + */ + if (is_lru_add && folio_ref_freeze(folio, 1)) { + folio_unqueue_deferred_split(folio); + fbatch->folios[i] = NULL; + folio_batch_add(&free_fbatch, folio); continue; + } folio_lruvec_relock_irqsave(folio, &lruvec, &flags); move_fn(lruvec, folio); @@ -176,6 +199,13 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn) if (lruvec) lruvec_unlock_irqrestore(lruvec, flags); + + /* Cleanup filtered dead folios. */ + if (is_lru_add) { + mem_cgroup_uncharge_folios(&free_fbatch); + free_unref_folios(&free_fbatch); + } + folios_put(fbatch); } @@ -964,6 +994,10 @@ void folios_put_refs(struct folio_batch *folios, unsigned int *refs) struct folio *folio = folios->folios[i]; unsigned int nr_refs = refs ? refs[i] : 1; + /* Folio batch entry may have been preemptively removed during drain. */ + if (!folio) + continue; + if (is_huge_zero_folio(folio)) continue; -- 2.52.0